The invention concerns heating of bodies in general by induction especially for purposes of cooking food.
It is well known that considerable development has taken place in high-frequency induction heating.
In an internally situated conductor, an AC-wound solenoid generates eddy currents the entity of which increases as AC frequency rises.
In the presence of a high frequency, therefore, eddy currents greatly increase and can be used for ovens, hotplates and the like.
Another well-known and effective way of using heating created by induced current is that of associating a wire gauze of ferromagnetic material to the base of receptacles suitable for containing objects, such as food and other things, to be cooked, which material, by its very nature, heats up under the effect of an induction field, transmitting the heat to the receptacle and therefore to the food or anything else in said receptacle. This system of heating presents a problem in that the wire gauze is insufficiently integrated in the base of the receptacle and can easily become detached from it partly due to uneven dilation between the base of the receptacle and the wire-gauzexe2x80x94the two being of different materialsxe2x80x94but also to warping of said base if the receptacle is made by die-casting. Both drawbacks considerably lessen the efficiency of the system.
The invention here described eliminates or greatly reduces said problems as will now be explained.
Subject of the invention is a system for induction heating and for cooking bodies in general, especially food, in a receptacle so heated, by application of an insert, consisting of a thin piece of ferromagnetic material, to the base of the receptacle.
The insert is integrated in said base becoming deeply embedded in it. The base is then ground and polished so that the outer surface including the ferromagnetic material is perfectly smooth.
The insert advantageously consists of a ferromagnetic wire gauze.
The wire gauze may be of the type known as stretched.
Alternatively the insert may consist of a closely perforated ferromagnetic sheet, the holes being round, square or of some other shape.
In one type of execution the insert may be embedded by placing it inside a die for casting a receptacle of non-ferrous material such as aluminium, nickel, cobalt, copper and alloys thereof.
The insert is placed in the die so that, after casting, it is fully covered by the base of the receptacle. This complete coverage at the base of the receptacle may be achieved by placing spacers in the bottom of the die in order to create a certain thickness between the insert and the external surface of said base.
The spacers are chosen for their magnetic properties if the die is to be placed vertically.
In one type of execution the insert is cast into an aluminium base which is then applied to a steel cooking pan.
In one type of execution the insert is incorporated into the base of a receptacle made of PTFE using suitable means for placing it on the bottom of the die into which the PTFE is poured to cast the receptacle.
In one type of execution the insert is incorporated into the base of a receptacle made of Tetrafluoroethylene Polymer (PTFE) using suitable means for placing it on the bottom of the die into which the PTFE is poured to cast the receptacle.
In another type of execution the insert is incorporated in the base of an earthenware or glass receptacle.
The invention offers evident advantages.
Far greater heating efficiency is ensured by integration of the ferrormagnetic insert, whether this consists of a wire gauze or of an equivalently perforated sheet, into the base of the receptacle for heating or for cooking food, such integration being obtained by complete incorporation of the insert into the material of the receptacle.
The present probable detachment, over time, of the wire gauze from the base of an ordinary receptacle is avoided.
Grinding and polishing of the base at conclusion of the operation ensures a close surface match between an induction-heated hotplate and the base of the receptacle, therefore maximum interaction with the magnetic field and a much higher level of efficiency.
Characteristics and purposes of the invention will be made clearer by the following examples of its execution illustrated by diagrammatically drawn figures.